Apparatus for monitoring a cardiac rhythm during cpr

ABSTRACT

A defibrillator and method for using a defibrillator which adopts an ECG analysis algorithm that can detect a cardiac arrhythmia in the presence of noise artifact induced by cardio pulmonary resuscitation (CPR) compressions. The apparatus and method offers guidance throughout a cardiac rescue protocol involving both defibrillation shocks and CPR that improves the effectiveness of the rescue, resulting in more CPR “hands-on” time, better treatment of refibrillation, and reduced transition times between CPR and electrotherapy.

The invention relates to an improved apparatus and method for treatingvictims of cardiac arrest, and in particular for those patients whorequire a treatment regime consisting of cardiopulmonary resuscitation(CPR) and defibrillation electrotherapy.

A defibrillator delivers a high-voltage impulse to the heart in order torestore normal rhythm and contractile function in patients who areexperiencing arrhythmia, such as ventricular fibrillation (“VF”) orventricular tachycardia (“VT”) that is not accompanied by spontaneouscirculation. There are several classes of defibrillators, includingmanual defibrillators and automated external defibrillators (“AEDs”).AEDs differ from manual defibrillators in that AEDs can automaticallyanalyze the electrocardiogram (“ECG”) rhythm to decide if defibrillationis necessary. After deciding that a shock is needed, the AED arms itselffor delivering an electrotherapeutic shock, and then the AED advises theuser to press a shock button to deliver the defibrillation shock. An AEDthat operates in this manner is called semi-automatic. Fully automaticAEDs deliver the defibrillation shock without any user input. Fullyautomatic AEDs are generally called fully automatic defibrillators inorder to reduce confusion in terminology.

FIG. 1 is an illustration of a defibrillator 1 being applied by a user 2to resuscitate a patient 4 suffering from cardiac arrest. Thedefibrillator 1 may be in the form of an AED or a fully automaticdefibrillator capable of being used by a first responder. Thedefibrillator 1 may also be in the form of a manual defibrillator foruse by paramedics or other highly trained medical personnel. Two or moreelectrodes 6 are applied across the chest of the patient 4 by the user 2in order to acquire an ECG signal from the patient's heart. Thedefibrillator 1 then analyzes the ECG signal for signs of arrhythmiawith a shock analysis algorithm. Only if a shockable rhythm, such as VFor a non-perfusing ventricular tachycardia (VT), is detected does thedefibrillator 1 arm itself to deliver a high voltage shock. Thedefibrillator 1 signals the user 2 via aural or visual prompts that ashock is advised. The user 2 then presses a shock button on thedefibrillator 1 to deliver a defibrillation shock.

It is well established that the quicker that circulation can be restored(via CPR and defibrillation) after the onset of VF, the better thechances that the patient will survive the event. For this reason, manyAEDs such as the one shown in FIG. 1 also incorporate a user interfaceincluding audible, aural, and visual prompting for guiding a userthrough a programmed sequence of CPR and defibrillation shocks. The userinterface may include detailed aural prompting for properly applying CPRcompressions, an audible metronome for guiding the user to the properrate of compressions, a visual display to show the state and progress ofthe event, annunciators, flashing lights, and the like. The sequence ispre-programmed into the device in accordance with a protocol establishedby the local medical authority.

There are several ECG analysis algorithms which automatically analyze apatient's ECG to decide if a defibrillating shock is appropriate totreat the underlying cardiac rhythm. One such algorithm is generallydescribed by Lyster et al. in the co-assigned U.S. Pat. No. 6,671,547entitled “Adaptive analysis method for an electrotherapy device andapparatus” and herein incorporated by reference. The described algorithmrelates to the Patient Analysis System (PAS) algorithm that is currentlyemployed in AEDs, such as the Heartstart™ FR3 AED manufactured byKoninklijke Philips, N.V. of Andover, Mass.

But PAS and other existing ECG algorithms for determining a shockablecondition require relatively noise-free ECG signals. All existingprotocol sequences require the cessation of CPR during analysis becauseCPR causes artifact in the ECG which can mask VF when it is occurring,or can appear as VF when VF is not occurring. The former conditioncauses an undesirable reduction in sensitivity of the analysis, whilethe latter condition causes an undesirable reduction in specificity ofthe analysis. Consequently, all existing protocols of CPR anddefibrillation require periodic “hands-off” periods of at least severalseconds to allow the defibrillator to analyze the ECG with sufficientaccuracy to be safe, useful, and effective to the patient.

Several problems arise from the need to interrupt CPR for ECG analysis.It has been shown that interruptions in CPR compressions, even for justa few seconds, may reduce the likelihood of a successful resuscitation.Thus, the required cessation of CPR for ECG analysis prior to deliveringa defibrillating shock may reduce the chances of a successful patientoutcome. And the delay in resuming CPR after defibrillation in order toassess the success of the shock may also impact the patient outcome.

Several prior art solutions to this problem have been developed, alldirected toward reducing the amount of delay. One solution, for example,is to remove CPR noise artifact from the ECG signal by the use ofadaptive filtering. Co-assigned U.S. Pat. No. 6,553,257 by Snyder et al.entitled “Interactive Method of Performing Cardiopulmonary Resuscitationwith Minimal Delay to Defibrillation Shocks”, and herein incorporated byreference, describes such an adaptive filtering method.

Another alternative approach for analyzing ECG in the presence of CPRnoise artifact involves wavelet transform analysis of ECG data streams.One example of this approach is described by Addison in U.S. Pat. No.7,171,269 entitled “Method of Analysis of Medical Signals” andincorporated herein by reference. The '269 patent describes the use ofwavelet transform analysis to decompose signals into heart andCPR-related signals. Another example of this approach is adopted byCoult et al. in International Patent Application No. PCT/US2012/045292entitled “Systems and Methods for Analyzing Electrocardiograms to DetectVentricular Fibrillation.” There, an electrocardiogram signal isinterrogated by a wavelet, such as a Morlet, Myers, or Mexican Hatwavelet, prior to being analyzed and stratified into a shockable ornon-shockable ECG.

Unfortunately, all of these approaches tend to be computationallyintensive and hence difficult to implement in a portable device. Somealso lack the accuracy necessary to reliably determine a shockablerhythm in the presence of CPR noise artifact while avoiding “falsepositive” shock decisions. These techniques are also susceptible toexternal electrical noise, such as line noise, and have not beenadopted.

For these reasons, other solutions have been developed to shorten theamount of “hands-off” ECG time needed to accurately determine ashockable rhythm. Co-assigned U.S. Pat. No. 7,463,922 by Snyder et al.entitled “Circuit and method for analyzing a patient's heart functionusing overlapping analysis windows”, also herein incorporated byreference, describes one such technique of using time-overlapped ECGdata buffers to arrive at a quicker shock decision. Unfortunately, theseprior art solutions serve only to reduce the delay time, but do noteliminate them entirely.

Another problem that arises from the existing inability to analyze ECGin the presence of artifact noise from CPR is that of refibrillation. Aportion of patients that are successfully defibrillated, i.e. revert toan organized cardiac rhythm or asystole, subsequently re-enter VFseveral seconds to several minutes later. Some of these patientsrefibrillate during the fixed duration CPR period in which no ECGanalysis is currently possible. Consequently, there is presently notreatment for addressing refibrillation except to wait for the protocolhands-off analysis period at the end of the CPR period. This delay intreating refibrillation is likely to be suboptimal for patient outcomes.

One-solution to the problem of refibrillation during CPR have beenproposed, involving a measure of cardiac “vitality” during CPR. One suchmeasure is the so-called “probability of Return of SpontaneousCirculation” (pROSC) score determined during CPR and described byJorgenson et al. in U.S. patent application Ser. No. 13/881,380 entitled“Defibrillator with Dynamic Ongoing CPR Protocol”, incorporated hereinby reference.

Another measure for predicting VF is the so-called Amplitude SpectrumArea (AMSA) Score described by Quan et al. in U.S. patent applicationSer. No. 14/211,681 entitled “Treatment Guidance Based on VictimCirculatory Status and Prior Shock Outcome”. These approaches, however,only offer an indication of whether CPR should be discontinued toperform an ECG analysis for defibrillation purposes. Thus, additionaldelays can be induced by these solutions.

The inventors have recognized the limitations afforded by the prior art,and have determined that what is needed is a technique for analyzing ECGin the presence of CPR noise artifact which provides a robust andreliable indication of a shockable rhythm. The needed technique musthave sufficient sensitivity and specificity to eliminate delays betweenCPR and defibrillation, and to treat refibrillation quickly after itoccurs. The technique must be computationally efficient such that it canbe incorporated into a portable medical device which is used real-timeduring cardiac emergencies. The present inventors have developed such atechnique.

In accordance with the principles of the present invention, a medicalapparatus and method are described which improves the treatment forcardiac arrest. In particular, the apparatus is a monitor ordefibrillator which incorporates an ECG analysis algorithm that canaccurately identify a cardiac arrhythmia that is treatable byelectrotherapy, even in the presence of noise artifact typicallyexperienced during CPR. Such an algorithm permits a more efficient andeffective delivery of electrotherapy while simultaneously increasing theeffectiveness of CPR by reducing interruptions.

An improved method is also described. The method provides for treatmentusing a combination of CPR and defibrillation shocks that ispersonalized to the patient and thus obviates the need for asub-optimal, pre-determined rescue protocol that is the same for allpatients regardless of underlying conditions and reactions during theresuscitation to CPR and shocks and other treatments (e.g., drugs).Increased “hands-on” CPR compressions time, earlier treatment ofrefibrillation, and reduced transition time between CPR andelectrotherapy result from the improved method. In addition, theimproved method may adapt itself to changes in the patient's conditionduring the rescue.

Also in accordance with the principles of the present invention, an AEDfor use during CPR is described comprising an input of an ECG signal, auser interface having at least one of an aural instruction output and avisual display, an ECG analyzer in communication with the input andoperable to determine a shockable cardiac rhythm in the presence ofCPR-related signal noise artifact from the input, and a memory forstoring instructions related to a CPR rescue protocol that includes aperiod for providing CPR compressions. The AED also comprises aprocessor operable to issue instructions to the user via the userinterface, and further wherein the processor issues instructions tointerrupt the CPR rescue protocol if the ECG analyzer determines thecardiac rhythm is shockable, wherein the ECG analyzer is operable todetermine the shockable cardiac rhythm in the presence of CPR-relatedsignal noise artifact from the input with a sensitivity of greater thanabout 70% and a specificity of greater than about 95%. The ECG analyzermay comprise a novel and inventive set of fixed-frequency band passfilters which operate to filter the CPR-related signal noise artifactfrom the ECG signal data.

Also in accordance with the principles of the present invention, theabove described AED also includes a high voltage charging circuit incontrollable communication with the processor, a high voltage energystorage source connected to the high voltage charging circuit, and ashock delivery circuit connected to the storage source, the deliverycircuit operable to deliver a therapeutic shock via an output of theAED, wherein the processor controls the charging circuit to fully chargethe storage source in response to the determined shockable cardiacrhythm before the processor issues instructions to interrupt the CPRrescue protocol. The AED is further enabled to arm and deliver a shocksimultaneously with the cessation of the CPR compressions.

Thus, the AED eliminates all non-safety related delay between cessationof CPR and delivery of a defibrillating shock. Given safe methods ofdelivering a shock during compressions, the AED is enabled to deliver ashock without cessation of compressions. One such safe method may beincorporated in an AED that is arranged to be a fully automaticdefibrillator which automatically delivers a shock at the appropriatetime in the cardiac rescue without operator action. There, it isenvisioned that a rescuer with protective electrically insulated glovesmay be able to continue compressions even through the defibrillatingshock, without harm to herself or undue therapeutic effect of thedelivered shock. Alternatively, the fully automatic AED may use methodssuch as electrode impedance monitoring to determine when the operator isnot touching the patient, and automatically deliver the shockaccordingly.

Also in accordance with the principles of the present invention, amethod for providing electrotherapy during the application of CPR isdescribed, comprising the steps of receiving an ECG signal from two ormore external electrodes in electrical contact with a patient, the ECGsignal data characterized by corruption from a CPR compressions noiseartifact, filtering the stream of signal data through a set of frequencyband pass filters disposed to separate the cardiac signal from the CPRcompressions noise signal, obtaining a stream of signal datacorresponding to a predetermined time segment, analyzing the separatedcardiac signal to determine whether a shockable cardiac rhythm existswith a sensitivity of greater than about 70% and a specificity ofgreater than about 95%, deciding that a shock is to be delivered by anelectrotherapy delivery circuit based on the analyzing step, arming anelectrotherapy delivery circuit responsive to the deciding step, andautomatically issuing a user prompt to stop CPR and deliver theelectrotherapy at the completion of the arming step. The method furtherdescribes steps of displaying on a visual display the detection of ashockable rhythm, and/or the progress of the defibrillator arming inresponse to the determined shockable rhythm.

IN THE DRAWINGS

FIG. 1 illustrates a defibrillator and its use during a cardiac rescue,according to the prior art.

FIG. 2a illustrates one process flow embodiment of the inventivealgorithm for analyzing ECG in the presence of noise artifact from CPRcompressions.

FIG. 2b illustrates a process flow for determining a shockable cardiacrhythm from the analyzed ECG, according to one embodiment of the presentinvention.

FIG. 3 illustrates the frequency characteristics of a set of filters forremoving CPR artifact and other signal noise from an ECG signal,according to the present invention.

FIG. 4 illustrates an example ECG output buffer from one of the filtersshown in FIG. 3, according to one embodiment of the present invention.

FIG. 5 illustrates an exemplary two-dimensional decision surface forclassifying a corrupted ECG signal as VF or undecided, according to oneembodiment of the invention.

FIG. 6 illustrates a functional block diagram of an externaldefibrillator according to the present invention.

FIG. 7 illustrates an exemplary visual display that indicates thecharging state of the device, according to the present invention.

FIG. 8 illustrates a user interface on the external surface of an AED,according to one embodiment of the present invention.

FIG. 9 illustrates a process flow for illustrating a continuous CPRrescue mode of operation, according to one embodiment of the invention.

FIG. 10 illustrates a process flow for illustrating a scheduled CPRrescue mode of operation, according to one embodiment of the invention.

FIG. 11 illustrates a process flow for illustrating a cardiac rescueprotocol which automatically shifts between a continuous and a scheduledCPR rescue mode of operation based on the progress of the rescue.

FIG. 12 illustrates a timeline view of audio and visual information thatprovided during a cardiac rescue in the continuous CPR rescue mode ofoperation.

FIG. 13 illustrates a timeline view of audio and visual information thatis provided during a cardiac rescue in the scheduled CPR rescue mode ofoperation.

FIG. 14 illustrates a process flow embodiment for a cardiac rescueprotocol which automatically shifts between two ECG analysis algorithmsbased on the progress of the rescue.

FIG. 15 illustrates a detailed process flow method for shifting betweentwo ECG analysis algorithms based on the progress of a cardiac rescue.

FIG. 16 is a flow chart that illustrates a method for truncating CPR infavor of providing electrotherapy during a cardiac rescue.

FIGS. 17a, 17b, 17c, and 17d illustrate exemplary embodiments of a userinput button and a visual display that displays information regardingthe underlying state of the AED operation and contextual labels disposedadjacent the buttons.

DETAILED DESCRIPTION OF THE INVENTION

The inventive shock advisory algorithm, called the Optimized ArrhythmiaRecognition Technology (ART), generally applies the principles of theafore-described wavelet transform analysis to a stream of ECG signals,but instead replaces the wavelet transform with a series offixed-frequency band pass filters. The set of band pass filters ispreferably constructed to have frequency windows shaped like theGaussian windows that are used to produce traditional Morlet wavelets.

The ART algorithm suppresses CPR artifact related noise by selectivelypassing relatively high frequency components of a potentially corruptedECG signal. ART is based on the inventors' realization that, while CPRand an organized cardiac rhythm can occur at similar repetition rates ofabout 1 to 2 Hz, typical CPR noise has relatively few high frequencycomponents in its signal, i.e. the signal tends to be a roundedwaveform. Cardiac activity tends to have relatively numerous highfrequency components due to the rapid polarization and depolarization ofthe heart over a single cycle. It is these high frequency componentsthat are to be captured and analyzed by ART.

Now turning to the illustrations, FIG. 2a illustrates a process flowembodiment of the inventive ART algorithm 200 for analyzing ECG in thepresence of noise artifact from CPR compressions. At step 202, themethod first receives an ECG signal, preferably from two or moreelectrodes which are arranged in electrical contact with a patient'sskin. The ECG signal is a time-varying voltage whose source is thepatient's heart as well as possibly voltages induced by CPR compressionsbeing applied to the patient. The signal may also include other artifactsignals that are external to the patient, such as patient jostling andmotion, external electrical noise, etc. The ECG signal is preferablydigitized into a stream of signal data.

At filtering step 206, the digitized ECG signal stream is processedthrough the ART filtering algorithm. Here, each data point in the signalstream is filtered through a set of first through fourth parallelfilters at first through fourth parallel filtering steps 206′ 206″ 206″and 206″″, each having a different band-pass characteristic. Each filteris preferably a Finite Impulse Response filter. The number of filtersand the band-pass characteristics of each filter may differ somewhatwithin the scope of the invention.

A preferred arrangement of ART filters 306 is as follows and is shown inFIG. 3. Four basic filters may be adopted, which generally apply to thecorresponding filter steps 206 in FIG. 2a . One, called FLATS 306′, andanother one, called CLAS1 306″, tend to pass higher frequency componentsof the ECG signal, and may present features to 1) distinguishventricular fibrillation from asystolic rhythms; 2) distinguishventricular fibrillation from organized cardiac activities; 3)distinguish ventricular fibrillation from asystolic rhythms andorganized cardiac activities. Both FLATS 306′ and CLAS1 306″ tend toattenuate data at frequencies associated with CPR artifact such thattheir outputs are of cardiac information that is separated from the CPRcompression noise signal. As can be seen in the illustrative andexemplary embodiment of FIG. 3, FLATS 306′ has a center frequency ofabout 35 Hz, and CLAS1 306″ has a center frequency of about 25 Hz. CLASS306″″ is arranged to reject radio frequency (RF) noise. And CLAS4 306′″may be arranged to pass lower frequency components that are useful forrejecting false positive indications of VF caused by certain artifacts,for instance, due to transportation, muscle contraction, radio frequencyinterference, etc.

In the preferred arrangement, the digitized ECG signal input results infour filtered ECG signal stream outputs.

As can be seen from FIG. 4, many oscillations exist in the filteredsignals, so that there are many zero and near-zero samples in thebuffer. In order to remove these effects, an additional envelope filtermay optionally be applied to the data in order to remove the localizedzeros and non-zeros. FIG. 4 illustrates the effects and the optionalenvelope filtering step 405 on the oscillating output 402 of the CLAS1filter 306″.

At buffering step 204, each stream of filtered ECG signal data issegmented into sequential time segments, i.e. buffers ECG1 ECG2 . . .ECGi. One preferred arrangement is non-overlapped adjoining buffers of3.5 seconds length. One sampling rate is 250 samples per second, whichequates to 875 samples of ECG per buffer. Time segment length andsampling rates are predetermined, and may differ within the scope of theinvention. Each of the data points from each buffer has a value,depending on the input and the underlying filter. An example of afiltered ECG buffer data set for CLAS1 is shown in FIG. 4.

It is preferred and advantageous that the buffering step 204 occursafter the filtering step 206. By filtering prior to buffering, themethod avoids filter transients at the edge of each buffer. Otherwise,the method would require longer, overlapping buffers which would entaillonger analyzing time with the attendant dilatory effects on patientoutcomes.

At step 208, data in each of the filtered ECG buffers is compared to athreshold value. The number of data points falling within the thresholdvalue for that filtered ECG buffer, called a score, is then calculatedfor use by the analyzing step 210. Of course, any mathematicalequivalent to the number of data points, such as a proportion or afraction, could be substituted within the scope of this method step. Forthe purposes of this illustration, the score for the filtered ECG bufferfor the FLATS filter is designated the FLATS score. The score for thefiltered ECG buffer for CLAS1 is designated the CLAS score. Accordingly,FIG. 2a illustrates that threshold comparisons step includes a thresholdcomparison for each of the parallel filtering steps, i.e. first throughfourth parallel threshold comparison steps 208′, 208″, 208′″, and 208″″.

Threshold values for each of the filtered ECG buffer scores may bearrived at in a number of ways, the determinations of which fall withinthe scope of the present invention. Thresholds may be fixed, e.g.predetermined, or may be adaptive, e.g. are calculated based upon a meanvalue of all of the data points in the particular buffer. For example,the FLATS buffer data set may be scored against a fixed threshold value,and the CLAS buffer data set may be scored against an adaptive thresholdvalue.

The analyzing step 210 begins by comparing the filtered ECG bufferscores to a predetermined decision surface. The decision surface, whichis constructed using databases of ECG signal data having CPR corruptionnoise, defines whether a given set of buffer scores indicates “VF” or“undecided”, i.e. other than VF. One example of a decision surface inthe CLAS and FLATS dimensions is illustrated in FIG. 5. In that example,decision surface 510 is constructed of corresponding pairs of one of theCLAS scores and FLATS scores. Score pairs that fall within the decisionsurface 510 indicate a VF condition. Score pairs that fall outside thedecision surface 510 indicate an undecided condition. Additionaldimensions of decision surface may be added using threshold values foradditional filtered ECG buffers as desired to create a more accurate VFdecision. Although only two dimensions are shown here, three or moredimensions may be used for a decision surface that incorporates theother CLAS scores as well.

Analyzing step 210 proceeds by comparing two or more buffer scores thatrepresent the particular cardiac signal characteristics to the decisionsurface in order to determine VF or other than VF. For the example shownin FIG. 5, an example pair of CLAS/FLATS score is shown at 520,indicating VF. The value pair 530 that falls outside the decisionsurface 510, e.g. above and/or to the right, indicates an undecided,i.e. other than VF, condition.

Each original time-segmented ECG buffer can thus be designated as “shockadvised”, i.e. corresponding to VF, or “undecided”, i.e. correspondingto “other than VF”. Once the ECG buffer is determined as shock advisedor undecided, ART repeats the steps of capturing, obtaining, filtering,and analyzing for the next ECG buffer in the time sequence as shown in“select next ECG buffer” step 212. The process of repeating enablesadditional methods of combining each new buffer with previous buffers togenerate an overall continuous determination of the presence of VF ornot.

The above-described method has been shown to identify VF with anaccuracy that is sufficient to safely make a shock determination duringthe application of CPR, and without the need for further confirmation ofthe analysis during a “hands-off” time. The sensitivity of ART to VF fora single buffer of CPR-contaminated ECG has been demonstrated to exceed70%, i.e. ART will detect true VF more than 70% of the occurrences.Similarly, the specificity of ART has been demonstrated to exceed 95%for a single buffer of ECG, i.e. will not generate a false positive VFindication from more than 95% of “other than VF” occurrences.

It may also be noted that the ART performance during “quiet” periodsapproaches that already demonstrated in the existing PAS algorithm. Thesensitivity of ART to VF on ECG data that is not contaminated with CPRartifact exceeds 80%, as compared to PAS on similar data at about 94%.Specificity of ART and PAS to false VF on a buffer of “clean” ECG isnearly identical.

Now turning to FIG. 2b , the method continues. One preferred embodimentof the method comprises the afore-described steps 202-212 as beingperformed in a separate processor, such as a DSP, from the stepsmentioned in the following several paragraphs. Such an arrangementallows each ECG buffer in turn to be analyzed and classified as VF or“undecided” relatively independently of the shock decision and controlprocessor, which primarily needs only the stream of classifications datafrom the ECG signal stream. Another preferred embodiment of the methodcomprises further separation of processing into multiple components. Forexample, digitization of the ECG signal input at step 202 could behandled in a front end chip such as an ASIC, the digital stream fed intoa DSP for filtering the digitized ECG signal stream into the separatefiltered streams corresponding to method step 206. Yet another processorwould then receive the filtered streams for final classification,decision-making, and response handling functions that will be describedin the following paragraphs.

If VF is determined from the ECG buffer at analyzing step 210, i.e. a“shock advised” outcome, then the underlying ECG rhythm is generallyassumed be a shockable cardiac rhythm. But the optimal response to a VFdetermination may not simply be to prepare the underlying device toprovide electrotherapy. Instead, it may be preferable to obtainconfirming determinations, or to otherwise to convey the determinationto the user in some manner that does not unduly disrupt the ongoingcardiac rescue. A separate deciding step 214 is thus warranted for thesepurposes, and is shown in FIG. 2b as taking input from analyzing step210. Examples of such situations will be provided in followingparagraphs.

Because ART sequentially analyzes multiple ECG buffers during aminutes-long CPR period, accumulated sensitivity to an ongoing patientcondition of VF will increase, i.e. more chances to detect a true VFcondition. But it is also expected that accumulated specificity willdecrease, i.e. more chances to mistake an “undecided” condition as VF.In order to maintain the specificity of the overall method at anacceptable level over this relatively long period of time, optionalmultiple-buffer rules may be developed for making a shock decision fromVF/undecided decisions over time-consecutive ECG data buffers. Therepeated, second analyzing step 210 of an ECG buffer of a later, secondpredetermined time segment is provided to the deciding step 214.Deciding step 214 then additionally bases its final decision on thesecond analyzing step.

For example, the analyzing step 210 may determine that a cardiac rhythmis shockable only if three time-consecutive ECG buffers indicate VF.Otherwise, the analyzing step indicates a non-shockable rhythm. It hasbeen shown that, under these rules, ART maintains a specificity of >95%over long periods of CPR, while sensitivity remains >70%. In some cases,sensitivity can exceed 95% and specificity can exceed 98%. Suchperformance is acceptable for making shock decisions during CPR periods.In summary, whereas deciding step 214 essentially receives an ongoingstream of VF/undecided ECG buffer, the step 214 applies the rules forthe final decision that the underlying device should operably proceed tothe delivery of a defibrillating shock.

A displaying step 215 may be initiated immediately upon thedetermination, such as a visual graphic or textual message on a display,a light signal, or a subtle audible signal. Preferably, the displayingstep 215 is provided even before the device is fully prepared to deliverelectrotherapy, but in an unobtrusive manner that does not distract theuser from continuing CPR compressions up until the device is ready forshock delivery. On the other hand, there are some modes of operation inwhich it may be preferable not to provide any information at all to theuser of a shock determination until arming is complete. Some lay usersmay be unnecessarily distracted or startled from providing CPRcompressions at the mere indication that the device is preparing todeliver a shock.

Responsive to a determination from deciding step 214 that a shockablecardiac rhythm exists and that electrotherapy should be provided, anarming step 216 begins. Arming step 216 may consist of charging a highvoltage charging circuit with sufficient energy to defibrillate apatient. Arming step 216 may include an audible and/or visual indicatorthat the arming step has begun, along with some indication as to theprogress toward being fully prepared for shock delivery, step 217. Forexample, dynamic bar graph indicia 720 on a visual display 700 may showthe progressive filling of a bar graph corresponding to the increasingcharge state of the high voltage circuit. A text message 710 on display700 may also indicate that charging is ongoing. An ECG display 730 maybe displayed on the charging state display simultaneously with theprogress indicators. FIG. 7 illustrates one exemplary embodiment of sucha display 700. An audible progress indicator could comprise a continuoustone of rising frequency which stops when a fully charged state isattained.

At the completion of arming step 216, the electrotherapy device is fullyprepared to deliver a shock. After arming, it is preferable that a stepof automatically issuing a user prompt 219 to stop CPR for the deliveryof electrotherapy occurs. An audible prompt from a speaker 830, anilluminated or flashing shock button light 820, and/or a displayindication 802 may be used to signal the user to stop CPR for shockdelivery. See FIG. 8 for an example of these indicators on a userinterface 818. In the case of an AED, the prompt may also instruct theuser to press the shock button 892 to deliver a shock. In the case of afully automatic defibrillator, a shock may automatically be deliveredimmediately after the prompt occurs, still at step 219. If the user isemploying electrically insulated gloves or other such protective gear,any prompting to “stop CPR” at step 219 may optionally be omittedaltogether.

In some circumstances, it may be desirable to delay the issuing of theuser prompt to stop CPR at step 219 until a minimum amount of CPR hasbeen provided. For example, it may be desirable to conduct at least 30seconds of uninterrupted CPR prior to delivering a shock. Optional delaystep 218 may be incorporated to the inventive method in order to ensuresuch a minimum CPR time.

Immediately after the delivery of electrotherapy, the user may beautomatically prompted to resume CPR at step 222. The device mayoptionally be enabled to detect the delivery of electrotherapy, at step220. Detecting delivery can be obtained by sensing outgoing current, abutton press, or the like. Then the method process returns to the stepsof capturing, obtaining, filtering, and analyzing in accordance with thestate of the cardiac rescue.

The method steps described above allow CPR to continue right up untilthe moment of delivering electrotherapy, and then to resume CPRimmediately thereafter. The result is that the proportion of “hands-on”time during a cardiac rescue is increased, thereby improving theeffectiveness of the overall treatment. Idle time waiting for a“hands-off” ECG analysis can be essentially eliminated, thereby avoidingthe loss of blood pressure and flow that occurs so quickly uponcessation of CPR. These benefits can be realized along with the method'sability to treat a reversion to VF during the CPR period. Ifrefibrillation occurs, the method simply detects the VF and prepares forelectrotherapy in the midst of the ongoing CPR compressions.

Other advantages are afforded by the inventive method. The inventorshave discovered that the use of filters instead of wavelets somewhatreduces the computational load required to analyze for VF, and moreeffectively suppresses interference by power line noises or similarhigh-frequency noises. Most of the method steps can thus be accomplishedin a single digital signal processor (DSP) that is arranged to receivethe ECG signal stream, to process the stream, and then to output acontinuous, time aligned and transformed ECG data stream. The DSP canalso operate in parallel with a second processor that controls the finalshock decision and delivery sequence in the AED. Also, the series offilters can be easily adjusted to also provide more robust rejection ofsignals induced by DC offsets, 50 Hz and 60 Hz external power-linenoise.

The afore-described method can be implemented in a medical device suchas an external defibrillator. FIG. 6 is a functional block diagram of anexternal defibrillator 10 according to the one embodiment of the presentinvention. Defibrillator 10 is configured as an AED that is intended foruse during a cardiac rescue which includes CPR. It is designed for smallphysical size, light weight, and relatively simple user interfacecapable of being operated by personnel without high training levels orwho otherwise would use the defibrillator 10 only infrequently. Althoughthe present embodiment of the invention is described with respect toapplication in an AED, other embodiments include application indifferent types of defibrillators, for example, manual defibrillators,fully automatic defibrillators, and paramedic or clinicaldefibrillator/monitors.

Defibrillator 10 receives an input 12 of an ECG signal from, forexample, two or more electrodes 16 that are connected to a patient. AnECG front end circuit 14 is in electrical communication with the input12 via a connector plug and socket or the like. The ECG front endcircuit 14 operates to amplify, buffer, filter and optionally digitizean electrical ECG signal generated by the patient's heart to produce astream of digitized ECG samples. The digitized ECG samples are providedto a controller 30, which may be a processor that combines a DSP and ARMprocessor. One exemplary controller is the family of ApplicationsProcessors manufactured by Texas Instruments Incorporated Inc. In oneembodiment of the apparatus, the DSP conducts all of the previouslydescribed filtering under the ART protocol, and then passes the multiplestreams of filtered ECG data to the ARM processor. The ARM buffers thestream of digitized ECG signal data into segments (buffers)corresponding to a predetermined time. The ARM performs an outcomesanalysis on the filtered ECG data to detect VF, shockable VT or othershockable rhythms. In accordance with the present invention, the ARMuses the outcomes analysis to determine a treatment regimen which ismost beneficial to the patient. These controller 30 portions of the DSPand ARM thus operate together as an ECG analyzer 32 as described in theabove method steps 202 through 222. Of course, the scope of the presentinvention is not limited to a particular DSP/ARM configuration. Theforegoing and following functions may be equivalently implemented in asingle processor or distributed among multiple processors.

ECG analyzer 32 incorporates an analysis algorithm that can determine ashockable rhythm in the presence of CPR-related signal noise artifactwith a sensitivity of greater than about 70% and a specificity ofgreater than about 95%. The accuracy of the ECG analyzer is sufficientto safely and effectively assess the cardiac state of the input signalin the presence of CPR compressions noise. One such analysis algorithmis ART as described previously.

If ECG analyzer 32 determines a shockable rhythm in combination with thedetermination of a treatment regimen that indicates the need for adefibrillation shock, then processor 34, responsive to the output of ECGanalyzer 32, sends a signal to a HV (high voltage) charging circuit 60to charge a HV energy storage source 70 in preparation for delivering ashock. When the HV energy storage source 70 is fully charged, processor34 directs a shock button 92 on a user interface 818, FIG. 8, to beginflashing to re-direct the attention of the user from the task ofproviding CPR compressions to the task of delivering electrotherapy.

As will be described in more detail, processor 34 can initiate thepreparation for a defibrillating shock immediately upon detection of ashockable cardiac rhythm, i.e. in a continuous mode of operation, andissue instructions to interrupt of CPR compressions for electrotherapyas soon as the device is armed. Alternatively, the processor 34 caninitiate preparation for a defibrillating shock prior to the end of apredetermined period of CPR compressions, and can instruct the immediatedelivery of electrotherapy simultaneously with the end of thepredetermined period. This last mode is called a scheduled mode.

In either continuous or scheduled mode, processor 34 controls the userinterface 18 to issue aural prompts to stop CPR and press the shockbutton to deliver a defibrillating shock. These prompts should be issuedtogether and in quick order so that delay between stopping CPR andpressing the shock button is minimized. The user interface 18 shouldsimilarly issue an aural prompt via audio speaker 20 to resume CPR assoon as possible after the processor 34 senses that a defibrillatingshock has been delivered, e.g. by sensing the button press, current flowfrom the HV storage circuit, etc. corresponding visual prompts may beissued simultaneously with the aural prompts.

When the user presses the shock button 92 on the user interface 818, adefibrillation shock is delivered from HV energy storage source 70through a shock delivery circuit 80. In a preferred embodiment, shockdelivery circuit 80 is electrically connected via an output of the AEDto the same electrodes 16 which receive the raw ECG signal.

Processor 34 also provides control of the user interface (UI) outputfunctions in the device. The user interface 18 is the primary means forguiding the user through the progress of the cardiac rescue protocol,and so includes at least one of an aural instruction output and a visualdisplay. In particular, user interface 18 may comprise an audio speaker20 to issue an aural verbal or signal prompt to the user regarding astate of the rescue, an instruction as to a next step to be taken in therescue, or regarding instructions responsive the determined shockablecardiac rhythm. User interface 18 may also convey audible informationvia a beeper 24. User interface 18 may also provide visual text orgraphical indications on a display 22. User interface 18 may also conveyvisual information via flashing light LED 26, which may illuminateadjacent graphics or buttons to be pressed. Preferably, processor 34controls the user interface such that each of these cues is provided ina manner that optimizes the desired response of the user. Audible andvisual cues pertaining to the same information need not be issuedsimultaneously if one or the other cue may detract from the desiredresponse. For example, processor 34 may control the charging circuit tofully charge the HV storage source to the armed state prior to issuingany instructions at all. Alternatively, processor 34 may drive the userinterface to indicate a determination of a shockable cardiac rhythm onvisual display 22 prior to issuing related aural instructions on speaker20. And again with reference to FIG. 7, processor 34 may drive the userinterface to indicate the state of the HV charging circuit prior toissuing related aural instructions on speaker 20.

Software instructions for operating controller 30 are disposed in anonboard memory 40. Instructions in non-volatile memory may include thealgorithm for the ART algorithm, the algorithm for PAS, instructions fora CPR rescue protocol that includes a period for providing CPRcompressions, UI configurations for multiple user types, and the like.Volatile memory may include software-embodied records of deviceself-tests, device operating data, and rescue event audio and visualrecordings.

Other optional features of the defibrillator shown in FIG. 6 include aSystem Monitor Controller which receives signals from various Buttons(e.g. Power On, Shock) and provides signals for the beeper and LEDlights. State changes of the buttons and sensors are transmitted back tothe processor 34 through a communications interface. This featureenables very low-power standby operations with wake-up sensing by meansof the button actuation and readiness status outputs.

FIG. 8 illustrates a structural embodiment of a user interface 818 onthe exterior surfaces of an AED 800 which corresponds generally to theuser interface 18 of the FIG. 6 functional block diagram. User interface818 may include a visual display 802 which provides graphic and textualinformation pertaining to the state of the cardiac rescue. Userinterface 818 may also include a speaker 830 which issues aural andaudible prompts. An LED 840 may provide a light-based signal forreadiness or malfunction. User interface 818 may also include first,second and third configurable buttons 854, 856, 858 whose functionchanges depending on the state of the rescue or on the configuration ofthe device. The configurable buttons functions may further be indicatedby contextual labels 804, 806, 808 displayed on visual display 802. Forexample, if the device is configured for an advanced operating mode,display 802 may indicate that an adjacent configurable button 854 isconfigured as an “analyze” button 94. Analyze button 94 may operate totruncate an ongoing rescue protocol. Truncation immediately ceases a CPRperiod and prepares the defibrillator for immediate delivery ofelectrotherapy. Embodiments of the analyze button 94 and itsfunctionality will be described in more detail below.

The preferred embodiment of the invention comprises the defibrillator 10that operates in a CPR rescue protocol, the operation characterized inthat apparatus-caused delay between providing CPR compressions anddelivering electrotherapy is eliminated. In order to achieve thisresult, the ECG analysis algorithm as described above is incorporatedwhich can accurately determine a shockable cardiac rhythm, without unduefalse alerting, even in the presence of motion-related signal noiseinduced by CPR compressions. ART is such an algorithm. ART allows thebackground detection of a shockable cardiac rhythm, the charging of theHV storage circuit and the arming of the device while CPR compressionsare being applied. The defibrillator is then ready to deliver a shocksimultaneously with the cessation of CPR compressions.

Modes of Operation Enabled by the Inventive Method and Apparatus

The defibrillator as described above can be configured with any ofseveral different modes of operation. The novel modes of operation aremade possible as a result of the inventive analysis method. The modes ofoperation address various new issues which may arise under the adoptionof the inventive method in the inventive apparatus.

Each mode of operation may be pre-loaded into the defibrillator memory40. An administrator or user of the device can select the desired modeduring device setup prior to the cardiac rescue. The particular mode isselected according to local rescue protocols and/or preference of themedical director for that locality.

The Continuous CPR Mode of Operation

FIG. 9 illustrates one embodiment of a continuous CPR rescue mode ofoperation 900. When the defibrillator is configured in a continuousmode, its processor always initiates a defibrillating shock whenever ARTdetects VF and the processor makes a shock decision. In the context ofthe following description, the term “continuous” is deemed to mean theimmediate application of defibrillation therapy whenever a shockablerhythm is detected. This particular mode of operation may also bereferred to as “Analysis through CPR custom” mode.

Continuous CPR rescue mode of operation is entered at step 902, wherethe ART algorithm has begun to evaluate the stream of ECG buffers. CPRcompressions may be ongoing at this time, but are not necessary to themode. The processor determines a shock decision at step 904, and if itdetermines a “shock advised” condition, the processor begins to preparethe defibrillator to deliver electrotherapy. Accordingly, the methodproceeds similarly to that described at FIG. 2b steps 215 through 222.

A shock advised displaying step 915 may be initiated immediately uponthe determination, such as with a visual graphic or textual message on adisplay, a light signal, or a subtle audible signal. Preferably, theshock advised displaying step 915 is provided even before the device isfully prepared to deliver electrotherapy, but in an unobtrusive mannerthat does not distract the user from continuing CPR compressions upuntil the device is ready for shock delivery. On the other hand, thereare some modes of operation in which it may be preferable not to provideany information at all to the user of a shock determination until armingis complete. Some lay users may be unnecessarily distracted or startledfrom providing CPR compressions at the mere indication that the deviceis preparing to deliver a shock.

Responsive to a determination from deciding step 904 that a shockablecardiac rhythm exists and that electrotherapy should be provided, anarming step 916 begins. Arming step 916 may consist of charging a highvoltage charging circuit with sufficient energy to defibrillate apatient. Arming step 916 may include an audible and/or visual indicatorthat the arming step has begun, along with some indication as to theprogress toward being fully prepared for shock delivery, at armingprogress displaying step 917. For example, dynamic bar graph indicia 720on a visual display 700 may show the progressive filling of a bar graphcorresponding to the increasing charge state of the high voltagecircuit. A text message 710 on display 700 may also indicate thatcharging is ongoing. An ECG display 730 may be displayed on the chargingstate display simultaneously with the progress indicators. FIG. 7illustrates one exemplary embodiment of such a display 700.

At the completion of arming step 916, the electrotherapy device is fullyprepared to deliver a shock. It is preferable that, immediately afterarming is complete, a step of automatically issuing a user prompt 919 tostop CPR for the delivery of electrotherapy occurs. An audible promptfrom a speaker 830, an illuminated or flashing shock button light 820,and/or a display indication 802 may be used to signal the user to stopCPR for immediate shock delivery. See FIG. 8 for an example of theseindicators on a user interface 818. In the case of an AED, the promptmay also instruct the user to press the shock button 892 to deliver ashock. In the case of a fully automatic defibrillator, a shock mayautomatically be delivered immediately after the prompt occurs, still atstep 919. The fully automatic AED may use methods such as electrodeimpedance monitoring or using the analysis algorithm to determine anabsence of CPR-related signal noise artifact to determine when theoperator is not touching the patient, and automatically deliver theshock accordingly. If the user is employing electrically insulatedgloves or other such protective gear, any prompting to “stop CPR” atstep 919 may optionally be omitted altogether.

Immediately after the delivery of electrotherapy, the user should beimmediately prompted to resume CPR at step 922 in order to minimizehands-off time. The device may optionally be enabled to detect thedelivery of electrotherapy, at step 920. Detecting delivery can beobtained by sensing outgoing current, a button press, or the like.

An optional step 924 of checking for the completion of a shock set maybe performed after step 922 and prior to returning to the shock decidingstep 904. A shock set is a predetermined number of electrotherapeuticshocks delivered within one period of continuous CPR rescue mode ofoperation. The predetermined number may be set by a medicaladministrator according to local preferences. A preferred number ofshocks in a shock set is three.

If the shock set completion checking step 924 determines that the shockset is complete, then the method exits the continuous CPR rescue mode ofoperation at exit step 926. Otherwise, the method proceeds to continuousmode end decision step 906.

Decision step 906 determines whether the duration of the continuous modeof operation has reached a predetermined time. Predetermined times maybe one minute or two minutes, or may be set at other desired times by amedical administrator according to local preferences. If the time hasbeen reached, the method exits the continuous mode at exit step 926.Otherwise, the method returns to the shock deciding step 904 forcontinued analysis of the next ECG buffer(s). The loop will continueuntil one of a shock set is complete or the continuous mode period iscomplete.

If a patient is responsive to electrotherapy, or never needs it at all,the AED operating in continuous mode will quietly analyze in thebackground while periodically providing appropriate guidance to checkthe patient or to continue CPR. The AED shock delivery circuit willnever unnecessarily be charged, thus saving battery power and extendingthe operating time. This mode may be particularly beneficial during usein commercial aircraft, where very-long-duration cardiac rescues aresometimes experienced during flight.

FIG. 12 provides an illustration of the informational outputs providedduring the continuous CPR rescue mode of operation. Time line 1200includes three rows along a horizontal axis representing the time in thecardiac rescue. The top row 1210 indicates the current state of thedevice. The middle row 1220 indicates the audible prompts that areissued by the device at the current state. The bottom row 1230 indicatesthe displays that are shown on the device user interface at the currentstate.

At the beginning of the rescue at deployment state 1212, electrodes maynot yet be deployed. An audible prompt 1222 and a visual display 1232 to“apply pads” are preferably provided simultaneously at this state inorder to emphatically instruct the user to perform this necessaryaction.

After the electrodes are deployed, the device will sense that it isreceiving ECG signals, and will enter the “analyzing during CPR” state1214. At this state, audio instructions and timing signals 1224 alongwith optional display information 1234 are provided to assist the userin providing effective CPR. During this time, the ECG analyzer and shockdetermination processor are operating.

If the device detects a shockable cardiac rhythm, the state enters thecharging and arming state 1216. Unlike prior art devices, however, theinventive device provides no, or only subtle, audible warning that ashock is advised and that the device is preparing itself to delivertherapy. Instead, CPR-related instructions at CPR state 1226 continue.This feature is particularly useful for the lay user having little priorexperience with a cardiac rescue. By refraining from audible promptsthat a shock is advised, the device forestalls the lay user, who may beconcerned about being shocked, from stopping CPR compressionsprematurely. An unobtrusive display message may instead be provided atcharging display state 1236 to indicate a charging state. As can be seenin FIG. 12, the ongoing CPR and device charging state may be displayedthere either textually or graphically or in some combination.

Only when the device is armed and ready to deliver a shock at state 1217is an audible prompt issued to the user at the “deliver shock” audibleprompt 1227. Simultaneously with the prompt, the shock buttonilluminates or flashes at state 1240 to attract the user's attention topress the button. An audible instruction such as “stay clear of thepatient, press the shock button now” is conveyed at this state.

After the shock button is pressed at state 1217, the rescue isimmediately resumed at a post-shock state 1218. An audible prompt to“resume CPR” 1228 is issued as soon as practicable after shock delivery,along with an appropriate display at 1238 which instructs the user toresume compressions. The rescue then loops back to state 1214 until orif another shockable rhythm is detected.

The Scheduled Mode of Operation

The scheduled CPR mode of operation appears familiar to a user of aprior art AED, but it actually functions in a significantly differentway. Unlike in the prior art AEDs, an AED functioning in a scheduled CPRmode of operation is analyzing the ECG even during CPR. But in thisscheduled CPR mode of operation, the AED refrains from issuing promptsto discontinue CPR regardless of the underlying sensed cardiac rhythm.Only after a predetermined and uninterrupted period of CPR has occurreddoes the device prompt the user to stop CPR and deliver a shock. The AEDimmediately, or at an appropriate time prior to the end of the period,prepares the device for electrotherapy upon a shockable rhythm detectionsuch that the device is ready to deliver a shock simultaneously with theend of the fixed period. This preparation preferably occurs in thebackground in order to reduce noise and confusion during CPRcompressions. In the context of the following description, the term“scheduled” can be deemed to mean the deferred application ofdefibrillation therapy to the end of a predetermined period even if ashockable rhythm is detected during the period. This mode is alsoreferred to as “:Analysis through CPR On.”

FIG. 10 illustrates one embodiment of a scheduled CPR rescue mode ofoperation 1000. When the defibrillator is configured in a scheduledmode, its processor delays the initiation of a defibrillating shockafter ART detects VF and the processor makes a shock decision. Thearming of the device for delivering electrotherapy is delayed until nearthe end of a predetermined period of uninterruptible CPR.

Scheduled CPR rescue mode of operation is entered at step 1002, wherethe ART algorithm has begun to evaluate a stream of ECG buffers aspreviously described. The AED may be providing via the user interfacevisual and aural user prompts to apply CPR compressions at this time,but this initial condition is not necessary to the mode.

The ART evaluations of ECG buffers may be distinguished from shockdecisions that are made from them. For example, in this scheduled CPRrescue mode, individual ECG buffer evaluations of “undecided” or “shockadvised” at step 1002 may be disregarded for therapy delivery purposesuntil the last portion of the scheduled mode period. Alternatively,these evaluations may be accumulated and used later in the period fordecision-making.

The processor determines a shock decision at step 1004. If step 1004determines a “shock advised” condition, the processor begins the processof preparing the defibrillator to deliver electrotherapy.

A shock advised displaying step 1015 may be initiated immediately uponthe determination, such as with a visual graphic or textual message on adisplay, a light signal, or a very subtle audible signal. Preferably,the shock advised displaying step 1015 is provided even before thedevice is fully prepared to deliver electrotherapy, but in anunobtrusive manner that does not distract the user from continuing CPRcompressions up until the device is ready for shock delivery. On theother hand, there are some modes of operation in which it may bepreferable not to provide any information at all to the user of a shockdetermination until arming is complete. This is because some lay usersmay be unnecessarily distracted or startled from providing CPRcompressions at the mere indication that the device is preparing todeliver a shock.

Responsive to a determination from decision step 1004 that a shockablecardiac rhythm exists and that electrotherapy should be provided, anarming step 1016 begins. Arming step 1016 may consist of charging a highvoltage charging circuit with sufficient energy to defibrillate apatient. Arming step 1016 may include an audible and/or visual indicatorthat the arming step has begun, along with some indication as to theprogress toward being fully prepared for shock delivery, at armingprogress displaying step 1017. For example, dynamic bar graph indicia720 on a visual display 700 may show the progressive filling of a bargraph corresponding to the increasing charge state of the high voltagecircuit. A text message 710 on display 700 may also indicate thatcharging is ongoing. An ECG display 730 may be displayed on the chargingstate display simultaneously with the progress indicators. FIG. 7illustrates one exemplary embodiment of such a display 700.

It is noted that the initiation of arming step 1016 may be timed suchthat the device reaches a fully armed state near the end of thepredetermined and uninterrupted period of CPR. This reduces thepossibility of an inadvertent shock being given to a provider of CPRcompressions. Regardless of when the arming begins, at the completion ofarming step 1016 the electrotherapy device is fully prepared to delivera shock, and at that time issues the instructions.

A delay step 1018 should be completed after arming. Delay step 1018 is apredetermined period of time from the entry of the scheduled mode thatensures that a full and uninterrupted period of CPR occurs before anypossible delivery of electrotherapy. Predetermined times may be oneminute or two minutes, or may be set at any desired time by a medicaladministrator according to local preferences. A preferred period of timeis two minutes, but may be in the range of from thirty (30) seconds orlonger.

After delay step 1018 is complete, a step of automatically issuing auser prompt 1019 to stop CPR for the delivery of electrotherapy occurs.An audible prompt from a speaker 830, an illuminated or flashing shockbutton light 820, and/or a display indication 802 may be used to signalthe user to stop CPR for shock delivery. See FIG. 8 for an example ofthese indicators on a user interface 818. In the case of an AED, theprompt may also instruct the user to press the shock button 892 todeliver a shock. In the case of a fully automatic defibrillator, a shockmay automatically be delivered immediately after the prompt occurs,still at step 1019. If the user is employing electrically insulatedgloves or other such protective gear, any prompting to “stop CPR” atstep 1019 may optionally be omitted altogether.

Immediately after the delivery of electrotherapy, the user should beimmediately prompted to resume CPR at step 1022 in order to minimizehands-off time. The device may optionally be enabled to detect thedelivery of electrotherapy, at step 1020. Detecting delivery can beobtained by sensing outgoing current, a button press, or the like. Step1020 may be employed to generate the resume prompt at step 1022. On theother hand, if step 1020 detects a lack of expected delivery of therapy,the device can respond by repeating the prompt, or by issuing adifferent prompt (not shown) that no shock has been delivered and thatCPR should be resumed immediately. Then at step 1026, the method exitsthe scheduled CPR rescue mode of operation.

If the ART algorithm determines that the ECG is undecided, it continuesto evaluate successive ECG buffers for a shock advised decision in theloop formed by decision step 1004 and an exit decision step 1006. Exitdecision step 1006 merely determines whether the predetermined period ofuninterrupted CPR is complete prior to returning to the analysis. Ifstep 1006 determines that the period is complete, the method exits thescheduled CPR rescue mode of operation at step 1026. The predeterminedperiod of uninterrupted CPR at step 1006 may be the same or a shorterduration than the period at step 1018.

By the above described method for scheduled mode and for a patient thatis responsive to electrotherapy, or who never needs it at all, the AEDoperating in scheduled mode will quietly analyze in the background whileperiodically providing appropriate guidance to continue CPR. The AEDshock delivery circuit will never unnecessarily be charged, thus savingbattery power and extending the operating time. This mode also may beparticularly beneficial during use in commercial aircraft.

Existing cardiac rescue protocols require at least a brief confirminganalysis and a HV charging time after CPR is complete. Without the delaybetween CPR and shock that is necessary in the prior art devices, thescheduled mode AED provides more effective treatment. The steps of thescheduled mode of operation may be visualized as a repeated cycle ofsteps 214-222 in FIG. 2b with the analysis steps of FIG. 2a alwaysoccurring in the background. The issued user prompt step 219 is alwaysdelayed at delay step 218 until CPR compressions have been provided fora continuous and predetermined fixed period of time.

The AED in scheduled mode may be desirable to medical administrators whovalue a high proportion of uninterrupted CPR in a cardiac rescue ascompared to treating a VF condition as rapidly as possible. The fixedperiod of CPR is also well known to responders, who value a consistentroutine during rescues, e.g. swapping duties during the rescue toforestall fatigue. The consistent routine, however, comes at the cost ofpossible delaying electrotherapy to a refibrillating patient.

In scheduled mode, the AED may issue aural instructions andnotifications differently than visual instructions in order to maintainthe consistency and “flow” of a CPR routine. The AED may for exampleconvey shock decisions and charging state only visually, so that arescuer is not unnecessarily distracted by audible prompts which mightinclude the distracting word “shock”. As the end of the CPR periodapproaches, the AED may only then issue guidance that a shockablecondition has been detected and that electrotherapy is ready fordelivery. Then, at the end of the CPR period, the AED may issue auraland visual instructions to “stop CPR and deliver a shock now” whilesimultaneously flashing the shock button 892. The guidance process thusminimizes the human delay between the end of CPR and shocking.

FIG. 13 provides an illustration of the informational outputs providedduring the scheduled CPR rescue mode of operation. Time line 1300includes three rows along a horizontal axis representing the time in thecardiac rescue. The top row 1310 indicates the current state of thedevice. The middle row 1320 indicates the audible prompts that areissued by the device at the current state. The bottom row 1330 indicatesthe displays that are shown on the device user interface at the currentstate.

The rescue states and the audible and visual prompts in the scheduledCPR rescue mode of operation generally correspond to the similarelements described above at FIG. 12 for the continuous mode. But thereis one significant difference that accords with the nature of thescheduled CPR rescue mode. If the device determines that a shock shouldbe delivered and subsequently prepares for delivery in the charging andarming state 1216, no further audible or displayed prompts indicatingthat a shock should be delivered are provided until an uninterruptibleCPR period 1350 has expired. The beginning of period 1350 coincides withthe beginning of that session of CPR at state 1214 and may last apredetermined time, such as two minutes. Only after the uninterruptibleCPR period 1350 has expired does the device begin to issue audible andvisual prompts to deliver a shock at state 1217.

Combined Continuous Mode and Scheduled Mode with Shock Sets

The AED may also combine continuous mode and scheduled mode in aprotocol that varies the proportion of electrotherapy opportunitiesrelative to CPR compressions throughout the course of a cardiac rescue.The response of the patient to the protocol may influence a shift to adifferent mode of operation. For example, if a patient is not responsiveto electrotherapy, an AED operating in continuous mode may not allow forenough uninterrupted CPR compressions time, so the AED may automaticallyshift to a scheduled mode instead. If a patient repeatedly experiencesrefibrillation, it may be desirable for the AED to maintain or revert toa continuous mode of operation to treat the condition more quickly.

A combined CPR rescue protocol 1100 method of operation with shock setsis described in FIG. 11. The combined method for providingelectrotherapy during the application of CPR includes a step 1107 ofautomatically shifting the protocol from a continuous CPR rescueprotocol to a scheduled CPR rescue protocol following the completion ofa predetermined number of shocks delivered during the continuous CPRrescue protocol. The predetermined group of shocks, all delivered withina single continuous CPR rescue protocol period, is called a shock set.The combined mode method may also include an automatic reversion fromthe scheduled to continuous mode after certain conditions are met.

The combined method begins at an entry step 1102, understood in generalto include providing a defibrillator having two or more externalelectrodes, a processor, a user interface and a shock delivery circuit.Entry step 1102 begins when the device is deployed activated, and hasits electrodes attached to a patient. The defibrillator may be one of asemi-automatic AED having a user-operated shock button, or may be afully automatic AED having an automatic delivery of electrotherapy.

The AED may be configured to provide one of several startup protocols oroperating modes when first activated at step 1102. The startup protocolmay be a “shock first” protocol in which an ECG analysis is conductedimmediately. If a shockable rhythm exists, the defibrillator arms itselffor an immediate shock. After electrotherapy is delivered, the deviceproceeds with its rescue protocol. Alternatively, the startup protocolor operating mode may be “CPR First” which regardless of the underlyingECG rhythm, the AED guides the user through an initial period ofuninterruptible CPR. This second CPR first startup protocol is shown atinitialization CPR mode step 1104. At step 1104 a user prompt isautomatically issued via the device user interface previously describedto apply CPR compressions.

If the user properly follows the step 1104 prompts to apply CPRcompressions, the ECG signal received by the device from the electrodeswill be characterized by corruption from CPR compressions noiseartifact. The afore-described algorithm such as ART analyzes thisreceived ECG signal to decide whether a shockable cardiac rhythm exists.

Initialization step 1104 may optionally include a predetermined periodof time, or an equivalent number of sensed compressions, before thedevice provides any guidance other than providing CPR compressions. Ashort initial period, such as between about 20 and 30 seconds or 30compressions, is believed to be beneficial to some patients prior todelivery of any electrotherapy. Initialization step 1104 exits to aninitial ECG shock decision step 1106.

Initial ECG shock decision step 1106 is also an optional step that isrelated to initialization step 1104. Step 1106 provides an initial shockdecision which may determine which of a plurality of CPR rescue modes isto be used next. For example, if the initial shock decision at step 1106is “undecided”, then it may be preferable to begin a conventional fixedduration of CPR compressions before any further electrotherapy. Thismethod step is indicated by the dashed line in FIG. 11 which proceeds toa scheduled CPR rescue protocol step 1000. But if the initial shockdecision at step 1106 is “shock advised”, then the method proceedsdirectly to a continuous CPR rescue protocol as indicated by step 900.

The combined method 1100 continues at step 900, wherein the devicebegins to operate in the continuous CPR rescue mode of operation. Themethod operates similarly to that previously described for thecontinuous mode, wherein responsive to a decision of a shockable cardiacrhythm in the analyzing step, the processor arms the shock deliverycircuit for delivering electrotherapy and then immediately issuesinstructions via the user interface to stop CPR for the delivery. And aspreviously described, the continuous mode method step 900 automaticallyends after the shock delivery circuit completes a predeterminedelectrotherapy shock set of a predetermined number of shocks deliveredwithin that step 900. Alternatively and as previously described, step900 ends if a lack of a determination of a shockable cardiac rhythm inthe analyzing step persists for a predetermined time. The exit thusoccurs responsive to the earlier of the predetermined time or after theshock delivery circuit delivers the predetermined number ofelectrotherapy shocks. And as previously described, an alternate exitmay occur responsive to a sensed predetermined number of CPRcompressions. At the exit, method 1100 automatically shifts atautomatically shifting step 1107 from operating in the continuous modeto operating in a scheduled CPR rescue mode of operation at step 1000.

Method 1100 operates according to the scheduled mode of operation asdescribed previously at step 1000. Here, responsive to a decision of ashockable cardiac rhythm in the analyzing step, the device processorarms the shock delivery circuit for delivering electrotherapy. After apredetermined period of uninterruptible CPR has passed, the processorissues instructions via the user interface to stop CPR for the delivery.After the predetermined period is complete, scheduled mode 1000 exits tocompletion of shock sets decision step 1108.

Method 1100 tracks the cumulative number of shock sets completed atprevious step 900. It is noted that this number does not necessarilycorrespond to the number of times that continuous mode at step 900 hasbeen entered or exited, because step 900 may exit due to the expirationof a predetermined time period instead of the completion of a shock set.If the exit is caused by expiration, for example, the shock counterwithin step 900 is reset. Thus each time continuous mode begins, anotherfull shock set or expiration of the predetermined time is necessary forexit.

Completion of shock sets decision step 1108 controls whether or notmethod 1100 reverts to the continuous CPR rescue protocol after the exitfrom the scheduled CPR protocol. Reversion occurs unless a predeterminednumber of shock sets has been completed, which corresponds to the numberof exits from continuous mode step 900 due to the completion of a shockset. If reversion occurs, steps 900 and 1000 are repeated. The cycleenabled by step 1108 repeats until the predetermined number of shocksets is completed. A preferred number of shock sets is three, and mayrange from one to seven.

This cycle between continuous and scheduled mode benefits those patientswho require prompt electrotherapy early in a rescue, such as forrefibrillating patients. But the cycle also enables the evolution to acardiac rescue sequence which provides uninterruptible full CPR periodsbetween shocks later in the sequence. Refibrillating patients that havenot responded to prompt electrotherapy thus begin to receive fullperiods of CPR.

If the predetermined number of shock sets has been completed,discontinuing step 1108 will discontinue further reversions. The methodinstead proceeds to a terminal scheduled CPR rescue protocol at step1110. At step 1110, all subsequent electrotherapy shocks will occursolely between intervals of uninterruptible CPR, i.e. after eachpredetermined period of uninterruptible CPR. When the CPR rescue iscomplete, the method 1100 ends by exiting at ending step 1126, which maybe initiated by manually turning the device off at an on-off button.

Apparatus Interleaving the Continuous and Scheduled Methods

A device, such as the AED shown in FIGS. 6 and 8 above, may operateaccording to any of the afore described methods for interleaving CPRwith electrotherapy. The AED is preferably controlled by processor 34which is in communication with the ECG signal input 12, user interface18, ECG analyzer 32, and memory 40 to provide instructional guidance tothe user in the conduct of a cardiac rescue.

Processor 34 in particular operates the AED in a sequence of continuousCPR rescue mode of operation and the scheduled CPR rescue mode ofoperation that is more beneficial to the patient than prior artsequences. When operating in the continuous CPR rescue mode of operationand if the ECG analyzer decides a shockable cardiac rhythm, theprocessor arms the shock delivery circuit for delivering electrotherapyand then immediately issues instructions via the user interface to stopCPR for the delivery. The AED processor immediately issues instructionsvia the user interface to resume CPR as soon as it senses the deliveryof electrotherapy in order to minimize “hands-off” time. When operatingin the scheduled CPR rescue mode of operation and if the ECG analyzerdecides a shockable cardiac rhythm, the processor arms the shockdelivery circuit for delivering electrotherapy. This arming occurseither immediately upon the decision or alternatively starts charging intime to be fully armed at the end of the period. After a predeterminedperiod of uninterruptible CPR, such as two minutes, the processor issuesinstructions via the user interface to stop CPR for the delivery.

Processor 34 is also responsive to the shock delivery circuit completinga predetermined electrotherapy shock set, after which the processorautomatically shifts from the continuous CPR rescue mode of operation tothe scheduled CPR rescue mode of operation.

The AED may be configured such that each electrotherapy shock setcomprises a predetermined number of shocks delivered within a singleinstance of the continuous CPR rescue mode of operation. In onepreferred embodiment, the AED may be programmable to set from two tofive shocks in each shock set.

Processor 34 may further be operable to automatically revert the AEDmode of operation from scheduled to continuous mode after one or moreinstances of scheduled CPR mode of operation. A sequence of modes thatcycles between continuous and scheduled modes can thus be established. Apreferred protocol is that the processor discontinues further reversionsafter the shock delivery circuit completes a predetermined number ofshock sets. The AED then remains in the scheduled mode and provideselectrotherapy shocks solely between intervals of CPR. In one preferredembodiment, the AED may be programmable to discontinue furtherreversions after from one to seven shock sets have been completed. TheAED may also be programmable to set the number shock sets to infinity,whereupon the cycle will continue until the device is turned off.

An optional embodiment of the AED processor operation is that theprocessor automatically shifts from continuous to scheduled CPR rescueprotocol if an “undecided” determination persists for a predeterminedtime. This operation would generally occur near the beginning of the AEDoperation such as at steps 1104, 1106 as shown in FIG. 11. If no suchdetermination persists, the processor will shift from continuous toscheduled mode according to the methods described above.

Another embodiment of the AED uses a sensed number of CPR compressionsparameter instead of elapsed time. The sensed number of CPR compressionsmay be obtained from one or more sources. Electrode noise artifactsignals or common mode current (CMC) may be used, external CPR sensingdevices such as the Q-CPR device manufactured by Philips ElectronicsNorth America, Andover Mass., may be used, or other similar sensors.

The AED and its operation as described above may be embodied in either asemi-automatic device or a fully automatic device. The semi-automaticAED of course includes a user-operated shock button 92 and thereforeshould include corresponding instructions and indications to press theshock button as appropriate. The fully automatic AED will embody aslightly different set of instructions that include nothing about theshock button but which clearly notify the user of a pending shock andthat instructs the user to remain clear of the patient if necessary.

Methods Using Two ECG Analysis Algorithms, Such as ART and PAS

The inventors have recognized that most patients never have a shockablerhythm during a cardiac arrest emergency, so any ECG analysis algorithmcould operate for long periods of time without providing a“shock-advised” determination. But the inventors also recognize that theafore described ART algorithm is not as sensitive to detecting ashockable cardiac rhythm as PAS. ART thus has a higher likelihood ofmissing “true positive” shockable rhythms during CPR. Also, the ART“undecided” determination does not distinguish between “no shockadvised” (NSA) and “indeterminate” ECG. For these reasons, it manybecome important during periods of CPR compressions to periodicallyconfirm the ECG analysis with a different ECG algorithm.

One solution to this problem would simply to use a PAS confirminganalysis periodically during the rescue. But this solution is suboptimalbecause it may unnecessarily increase the overall hands-off time. Theinventors have thus recognized that PAS can be used to confirm, butshould be used as infrequently as possible and only in those situationswhere hands-off time has minimal detriment to the patient. Suchsituations may be at the end of an otherwise scheduled period for CPRcompressions, for example.

FIG. 14 illustrates such a method solution that reduces the problemspresented by needlessly interrupting CPR compressions for a confirminganalysis. FIG. 14 is similar to FIG. 11. But FIG. 14 illustrates amethod that is modified to use both of a first ECG analysis algorithmand a second ECG analysis algorithm. The first ECG analysis algorithm isexemplified by the previously described ART algorithm 200, which isparticularly suitable for use in the presence of CPR-related signalnoise artifact. The second ECG analysis algorithm is exemplified by theexisting PAS algorithm, which is particularly suitable for use in theabsence of CPR-related signal noise artifact.

Like the FIG. 11 method, the illustration of FIG. 14 comprises a method1400 for providing electrotherapy during the application of CPR. Themethod is enabled at step 1102 in a defibrillator 1 having an ECG signalinput 12, a shock delivery circuit 80 and a user interface 18. Thedevice and method also utilize two different ECG analysis algorithms.The first, like ART, is operable to determine one of a “shock advised”(SA) and an “undecided” from the ECG signal while in the presence of aCPR-related signal noise artifact. The second, like PAS, can morespecifically determine one of a SA and a “No Shock Advised” (NSA)determination from the ECG signal in the absence of the CPR-relatedsignal noise artifact. The defibrillator in step 1102 senses that theECG signal input 12, such as electrodes, are attached and thus ready tobegin ECG analysis.

The FIG. 14 method proceeds at step 1104 by analyzing the ECG signalwith the first ECG analysis algorithm during a first period to determinewhether a shockable cardiac rhythm exists. It is preferable that thedefibrillator is providing CPR guidance instructions during this periodin a scheduled CPR rescue mode of operation. In the event of a SAdetermination, the defibrillator will prepare to deliver a shock at theend of the step 1104. In addition, the method proceeds at decision step1406 based on whether the ECG signal indicates a SA or an “undecided”determination. A preferred point for determination is at the end of thefirst period, although the determination could also be based on anaverage or count of SA's or the like over the period. Other aspects ofsteps 1102 and 1104 are previously described relative to FIG. 11 above.

If a SA is determined during the first period of decision step 1406,then the remaining steps of the CPR rescue procedure also correspond tothose described in the method of FIG. 11. In particular, following a SAdetermination, the cardiac rhythm is determined using the first ART ECGanalysis algorithm during second and successive periods of continuousCPR 900 and scheduled CPR 1000. Subsequent SA determinations cause thedefibrillator to arm for shock and issue CPR/shock delivery instructionsaccording to the type of CPR period. Shock sets may also be employed toshift from continuous to scheduled CPR modes of operation as previouslydescribed. Thus an optimized and customized rescue protocol is outputfrom the defibrillator.

Only if step 1406 determines any other than a SA determination is thesecond ECG analysis algorithm employed. If an “undecided” determinationoccurs at step 1406, the method automatically switches from the first tothe second algorithm at step 1407.

After switching step 1407, the method employs the second ECG analysisalgorithm (PAS) to analyze the ECG signal at PAS decision step 1410.Preferably, the defibrillator issues user prompt to “stop CPR” and/or“do not touch the patient” at this step so that the PAS algorithm caneffectively analyze in a low-noise environment. Two possible outcomes ofPAS decision step 1410 are SA or “No Shock Advised” (NSA). PAS may alsoissue an “artifact” decision, which is not a topic for this invention,and will not be further discussed.

A determination of SA in PAS decision step 1410 indicates that the ECGmay have presented as a shockable rhythm at or near the beginning of theevent, i.e. at step 1102, but that the first algorithm failed to senseit. A SA determination at this step is preferably followed by immediatearming and delivery of electrotherapy.

Evidence suggests that a patient with a SA presenting ECG rhythm maybenefit from more electrotherapy earlier in the rescue. Thus a SAdetermination by PAS in step 1410 also causes an automatic switch backto the first ECG analysis algorithm in a continuous CPR rescue protocol900 that delivers electrotherapy promptly after detection of a shockablerhythm. The continuous CPR rescue protocol 900 then functions aspreviously described.

But a determination of NSA at step 1410 indicates that the presentingECG is not shockable. Such patients may benefit from more CPRcompressions early in the rescue. Thus, an NSA determination by PAS atstep 1410 causes an automatic switch back to the first ECG analysisalgorithm in a scheduled CPR rescue protocol 1000 that delivers agreater relative amount of CPR time. The scheduled CPR rescue protocol1000 and the remainder of the cardiac rescue method then functions aspreviously described.

It is preferred that the duration of each period in which the PAS secondECG analysis algorithm operates is as short as possible because of thesub-optimal requirement that the rescuer is “hands-off” during theanalysis. A typical PAS analysis period is less than about ten seconds,although it may be as short as four seconds. This duration is in mostcases shorter than the duration of either a continuous or scheduled modeof CPR using the first ART algorithm. The frequency of the PAS periodsis also preferred to be as low as possible for the same reasons. Thus,the method steps require a switch to the “hands-off” PAS analysis onlywhen necessary to do so.

An alternative and more detailed view of the inventive method isillustrated in FIG. 15. The FIG. 15 method more clearly illustrates howelectrotherapy is provided with a minimum of interruptions to CPR, evenafter an initial ART algorithm period of CPR 1504. After activating thedefibrillator and applying electrodes at step 1102, an initializationperiod at step 1504 immediately begins, comprising the issuing ofprompts for applying CPR compressions and using the first ECG analysisalgorithm is. Step 1504 is preferably a scheduled CPR rescue mode ofoperation having uninterruptible CPR regardless of the ART rhythmdetermination. Step 1504 is even more preferably of a relatively shortduration of about 20-30 seconds, or enough time to apply a minimumnumber of about 30 CPR chest compressions. The method may sense thenumber of chest compressions or the amount of time, after which the ARTrhythm determination is finalized at decision step 1506. Step 1504 thusprovides all patients the benefit of some period of uninterrupted chestcompressions at the start of the rescue.

If SA is indicated at decision step 1506, then the method immediatelyenters an arming for electrotherapy step 1507, allowing for the deliveryof a therapeutic shock. Following step 1507, the method enters a secondperiod, continuous CPR mode of rescue protocol 900, which proceeds asdescribed previously. The duration of the second period 900 may be abouttwo minutes, but may also be configurable prior to device activation.Then the method proceeds to continuous mode terminal decision step 1509.

If a SA determination is present at step 1509, the method proceeds aspreviously described for the FIG. 11 method. The method enters an armingfor electrotherapy step 1511, allowing for the delivery of a therapeuticshock. Then the mode of operation with the first ART algorithmautomatically switches to a scheduled CPR rescue mode of operation atstep 1000. Step 1000 proceeds as previously described by prompting theuser with CPR instructions while analyzing the ECG rhythm in thebackground and by deferring any action from an SA determination to theend of the period. The scheduled period 1000 may be of about two minutesduration.

If a SA determination is present at the end of step 1000, i.e. atdecision step 1519, the method enters an arming for electrotherapy step1521, allowing for the delivery of a therapeutic shock. After the shockis delivered, the method may loop back to the continuous mode step 900if the shock sets are not yet completed at checking step 1108. If shocksets are complete, the method switches to the terminal scheduled CPRrescue protocol at step 1110, where it remains until the end of therescue at step 1126.

It can be seen by FIGS. 14 and 15 that as long as a SA state can bedetermined by the first ART algorithm, the method proceeds without theneed for the second PAS analysis. Thus, the method minimizes the“hands-off” time that is required for PAS.

If however the first ART algorithm instead determines an “undecided”state at any of the decision steps 1506, 1509, and 1519, the methodautomatically switches at respective steps 1520, 1530, and 1540 to thesecond PAS algorithm for a further determination. Steps 1520, 1530, and1540 issue “hands-off” instructions and then analyze the ECG. These PASperiods may be of short duration of ten seconds or less in order tominimize “hands-off” time.

As can be seen in FIG. 15, if any of the PAS analysis determinations areSA, decision steps 1522, 1532, and 1542 immediately return the method tothe first ART algorithm sequence at the respective point of departure,i.e. after step 1506, step 1509, or step 1519. The reasoning for thispath is that ART analyses are generally preferable to PAS analysesbecause of the overall reduced hands-off time. Thus the method shouldswitch back to ART whenever possible.

Also seen in FIG. 15 is if any of the PAS analysis determinations areNSA, then the method automatically shifts back to the first ARTalgorithm operating in a scheduled CPR mode of operation at step 1000.The reasoning for this path is that PAS has confirmed that the ECG ispresenting a non-shockable rhythm, and so for such patients a period ofuninterrupted CPR is more beneficial.

An optional step 1523 after any PAS determination of NSA sets thecurrent shock set as completed. This optional step thus moves the method1500 closer to a shift at step 1108 to a terminal and permanentscheduled CPR rescue mode of operation at step 1110. The reason for thisis the inventor discovery that an eventual shift to a higher proportionof CPR-to-shock in the scheduled mode may be more beneficial to apatient that indicates an NSA ECG rhythm somewhere earlier in therescue.

Apparatus Interleaving PAS and ART Algorithms in the Continuous andScheduled Modes of Operation

A device, such as the AED shown in FIGS. 6 and 8 above, may operateaccording to any of the afore described methods for interleaving CPRwith electrotherapy while incorporating two different ECG analysisalgorithms. The AED is preferably controlled by controller 30 whichincludes a processor 34 and an ECG analyzer 32. Controller 30 is incommunication with the ECG signal input 12, user interface 18, andmemory 40 to provide instructional guidance to the user in the conductof a cardiac rescue. Controller 309 also is in controlling communicationwith a shock delivery circuit 80 that delivers an electrotherapy output.

Memory 40 stores instructions related to both of a first ECG analysisalgorithm that is operable to determine one of a “shock advised” (SA)and “undecided” determination from the ECG signal in the presence of aCPR-related signal noise artifact from the input, and a second ECGanalysis algorithm that is operable to determine one of a SA and a “NoShock Advised” (NSA) determination from the ECG signal in the absence ofCPR-related signal noise artifact from the input. Memory 40 also storesinstructions related to a CPR rescue protocol that includes at least twoperiods for providing CPR compressions.

Controller 30 in particular operates the AED in the sequence ofcontinuous CPR rescue mode of operation and the scheduled CPR rescuemode of operation as previously described. In addition, controller 30issues guidance via the user interface 18 and automatically prepares theshock delivery circuit 80 for delivering electrotherapy responsive to aSA determination from either of the first and second ECG analysisalgorithms. Finally, and because the first ECG analysis algorithm mayhave a lower sensitivity to shockable ECG rhythms during periods withCPR-related noise, the controller 30 is further operable to alwaysautomatically switch from the first to the second ECG analysis algorithmat an end of one of the periods during which the first ECG analysisalgorithm determines any other than a SA determination. Thus, the use ofthe second ECG analysis algorithm, which requires “hands-off” time thatis sub-optimal for a cardiac arrest patient, is placed into use onlywhen necessary.

Other device behavioral aspects of the AED reflect the previouslydescribed methods. For example, if a SA is determined afterautomatically switching from the first to the second ECG analysisalgorithm, the AED controller may automatically switch back to the firstalgorithm and to a continuous CPR rescue mode of operation. On the otherhand, if a NSA is determined after automatically switching from thefirst to the second ECG analysis algorithm, the AED controller mayautomatically switch back to the first algorithm and to a scheduled CPRrescue mode of operation.

The second ECG analysis algorithm may be the PAS algorithm which cancharacterize an ECG rhythm in less than 10 seconds. The duration of eachperiod in which PAS operates should thus be no be longer than that.

The AED may functionally include the initialization period that occursjust after activating the AED and ECG signals are being received. Theinitialization period comprises a scheduled CPR rescue mode of operationusing the first ECG analysis algorithm, wherein the scheduled CPR rescuemode of operation provides a predetermined period of uninterruptible CPRregardless of the determination. The length of the initialization periodmay be relatively short as compared to subsequent rescue protocolperiods. For example, the initialization period may end at a sensednumber of CPR compressions, wherein the sensed number is about 30 andwhere in existing CPR protocols would be completed in less than 30seconds. Alternatively, the initialization period may be pre-determinedat a duration of between about 20 and 30 seconds.

The AED and its operation as described above may be embodied in either asemi-automatic device or a fully automatic device. The semi-automaticAED of course includes a user-operated shock button 92 and thereforeshould include corresponding instructions and indications to press theshock button as appropriate. The fully automatic AED will embody aslightly different set of instructions that include nothing about theshock button but which clearly notify the user of a pending shock andthat instructs the user to remain clear of the patient if necessary.

Analyze Button for Truncating CPR

There may be situations in which an experienced user may desire totruncate the ongoing AED protocol in order to quickly enter another modeof operation, and in particular to more quickly deliver a defibrillatingshock. The invention simplifies the truncating action by offering just asingle button to do so. The AED automatically selects the response tothe button press that is most beneficial to the patient, based on theunderlying ECG analysis.

A defibrillator (AED) and method for using a defibrillator incorporatesa user activated button which truncates an ongoing and otherwiseuninterruptible CPR compressions period to immediately perform adifferent defibrillator-related function. The truncation button isparticularly useful in the scheduled CPR rescue mode of operation 1000,previously described. Thus the operation is simpler for the user,reduces the potential for protocol-following errors, and minimizes delaycaused by confusion during the event.

One exemplary AED having a truncation feature may use two different ECGanalysis algorithms which have different sensitivities to a shockablecardiac rhythm. A press of the truncation button may automatically shiftfrom a first ECG analysis algorithm to a second ECG analysis algorithmhaving a higher sensitivity. The button may also allow truncation ofongoing analysis and CPR for immediate preparation for electrotherapy ifan underlying shockable cardiac rhythm has already been detected.

The AED and method reduce the hands-off time between CPR compressionperiods and electrotherapy, even when the truncation button isactivated. By way of example, if the underlying ECG analysis indicates ashockable rhythm, the AED may be charging for therapy in the background,while indicating “Charge” or “Analyze” on the truncation button. Thus ifthe user presses the truncation button, the AED may be ready to deliverelectrotherapy immediately.

The AED with the controlling features as previously described changesits response to a sensed press of the truncation button based on thecurrent state of the patient ECG. If the AED determines the underlyingECG to be shockable, it may change a contextual label for its button to“Charge”. When the AED senses that the truncation button has beenpressed, the AED immediately charges for a defibrillating shock. If theECG is non-shockable, the button label may instead appear as “Analyze”.Pressing the same button would cause the AED to immediately switch froma first ART algorithm to a second PAS algorithm to confirm the existingstate. Alternatively, a sensed truncation button press may immediatelycause the AED to issue a prompt to “stay clear of the patient” in orderto increase the sensitivity of the current ART algorithm analysis.

The method steps shown in FIG. 16 may be better understood by alsoreferring periodically to the particular visual displays and truncationbuttons shown in FIGS. 17a through 17d . FIGS. 17a, 17b, 17c, and 17dshow various graphic displays 1706, 1714, 1718, and 1728 correspondingto an AED visual display such as visual display 802. Each of the FIGS.17a-d shares a common general arrangement. One or more guidance andinformation messages are displayed on an upper banner area. A progressbar such as a CPR progress bar may be placed adjacent the upper bannerarea. In the center of the display is an area for showing an ongoing ECGtrace or guidance graphics for placing electrodes, hands on chest forCPR, and the like. The bottom portion of the display preferably includescontextual labels, exemplified by contextual labels 804, 806, that maychange based on the particular operating state of the defibrillator andthe underlying ECG analysis.

In a preferred embodiment, input buttons 854, 856 are disposedimmediately adjacent to displays 1706, 1714, 1718, and 1728, and next tocontextual labels 804, 806 respectively. In an alternate embodiment,visual display 802 may be a touch sensitive display such that the inputbutton 854,856 effectively underlies its respective contextual label804,806.

Now turning to the FIG. 16 flow chart, an exemplary method 1600 fortruncating CPR for the purpose of providing immediate electrotherapy isshown. The method begins at providing step 1602 of a defibrillatorhaving features which work in concert to perform the method. Namely, thedefibrillator includes an ECG signal input 12, a user interface 818including an input button 854 and a visual display 802, a shock deliverycircuit 80, and a first ECG analysis algorithm that is operable todetermine a shockable cardiac rhythm from the ECG signal in the presenceof a CPR-related signal noise artifact from the input. A defibrillatorsuch as AED 800 is but one example of the provided apparatus.

AED 800 may include several different operating mode configurationswhich are preconfigured prior to use. Any or all of these modes may bemaintained in the AED memory 40. Exemplary operating modes are AdvancedMode, CPR First Mode, and Semi-Automatic mode. Each operating mode maydiffer slightly as to the circumstances in which a truncation button mayappear.

Advanced Mode is a protocol that permits a responder more control overwhen the AED begins ECG rhythm analysis and arming for shock delivery.The Advanced Mode, for example, may be configured to provide an“ANALYZE” and/or a “CHARGE” option button at particular periods duringthe protocol. Pressing the “ANALYZE” option button may initiate animmediate Hands-Off Analysis with PAS. Pressing the “CHARGE” button maypermit one or more of a Hands-Off Analysis, charging of the high voltageenergy storage source 70, and shock delivery.

After the AED 800 activates and begins receiving an ECG signal input 12,it begins to analyze the ECG signal with the first ECG analysisalgorithm (ART) during an optional initial period 1604. Initial period1604 is preferably similar to step 1104 operating in an uninterruptibleCPR compressions mode of operation as described previously. During thisshort initial period 1604, however, the truncation button may be activeto immediately exit from CPR compressions to an ECG analysis or forarming for electrotherapy. The reason for enabling the truncation buttonat period 1604 is to allow for situations where the operator recognizesthat adequate CPR has been provided prior to the arrival and activationof the AED.

The visual display during initial period 1604 preferably corresponds toan “analyze-undecided” screen 1706 as shown in FIG. 17a . The AEDdisplays a contextual label of “Analyze” adjacent to truncation button854. If the operator wishes to truncate the initial compressions periodfor analysis, she presses the truncation button 854. When the AED sensesthe button press, it immediately issues user prompts to “stay clear ofthe patient” and begins an ECG analysis using the 2nd PAS ECG analysisalgorithm. During this time, the AED may display an “analyze-stay clear”screen 1728 from FIG. 17 c.

Label step 1606 follows optional step 1604. Label step 1606 sets theinitial contextual label that corresponds to a previously analyzed ECGat the initiation of the ART analysis period 1608. Preferably, the AEDdisplay the “analyze-undecided” screen 1706 in order to establish thenext steps in the protocol.

First analyzing period step 1608 follows label step 1606. Step 1608includes the device analyzing the ECG signal with the first (ART) ECGanalysis algorithm and preferably in the uninterruptible scheduled modeof CPR. Step 1608 thus includes the defibrillator issuing audible and/orvisual prompts to continue CPR compressions. The analyzed ECG signalduring this period will be either “undecided” or “shock advised” asshown at decision step 1610. Also during this first analyzing period,the defibrillator controller 30 begins to monitor for an activation ofinput button 854.

As can be seen in FIG. 16, the next steps in the method 1600 depend onthe underlying analyzed ECG signal. If the decision at steps 1608, 1610are “shock advised”, the left branch of the method proceeds. The AED maychange the upper portions of display 1706 to indicate the directive textat display step 1612. An information message such as “shock advised”and/or a guidance message of “Press Analyze Button” as shown on“truncation available—shockable rhythm” screen 1714 of FIG. 17b mayappear. Alternatively, a guidance message of “Press Charge Button” asshown on “truncation available—charge” screen 1718 of FIG. 17d mayappear. Audible guidance at this step 1612 is also possible but is lesspreferable than solely visual guidance in order to prevent unduedistraction from the task of providing CPR compressions. Alternatively,step 1612 may include issuing an audible instruction that the truncationbutton is active.

A “shock advised” decision at step 1610 may also initiate a change incontextual label 804 at contextual label change step 1614. Thecontextual label 804 may be changed from the “Analyze” indication to a“Charge” indication. Alternatively, the “Charge” contextual label/buttoncombination could be displayed with the “Analyze” indication at the2^(nd) contextual label 806 adjacent the second configurable button 856as seen in FIG. 17b . Then the AED may initiate a background charging ofthe HV energy storage source 70 at background charging step 1616.

With the analyzed ECG signal indicating a shockable rhythm, the AEDmonitors for a truncation button activation at sensing step 1618. If noactivation occurs, the method 1600 merely loops back to analyze step1608 for continued monitoring during the period.

If the AED senses the truncation button activation at sensing step 1618,the AED immediately proceeds to an armed shock delivery state. Chargingof the HV energy storage source 70 is completed if necessary at chargingstep 1620 and the shock button is armed at arming step 1622. Appropriatevisual and audible prompts are provided along the way to guide andinform the user.

Some users prefer to omit background charging of the HV circuitrywhenever CPR compressions are being provided. The AED thus can bepre-configured to omit background charging step 1616. In thisconfiguration, when the AED senses button activation at sensing step1618, it immediately proceeds to an operating state of charging theshock delivery circuit at charging step 1620. The AED then arms itselffor shock at arming step 1622.

Exit step 1624 exits the method after the AED is armed. Following exitstep 1624, other methods may proceed such as looping back to step 1608,entering different protocols, or the like.

The right branch of the method proceeds if the decision at steps 1608,1610 is “undecided.” “Undecided” is a determination of another-than-shockable rhythm, which includes non-shockable rhythms aswell as indeterminate rhythms. The first ECG analysis algorithm may alsobe unable to distinguish between a shockable and non-shockable cardiacrhythm, especially in the presence of CPR-related signal noise, and thuswould return an indeterminate “undecided” decision. The AED preferablydisplays the “Analyzing-undecided” visual display 1706, the “Analyze”contextual label 804, and active monitoring for a sensed press oftruncation button 854 at this state. Truncation button sensing step 1626actively monitors for the sensed press of the truncation button withoutany further prompting of the operator. It can be seen at sensing step1626 that the absence of a sensed press merely loops the process back tothe analyzing step 1608 for continued monitoring.

When the AED senses the truncation button press at sensing step 1626,the method immediately interrupts the ongoing CPR compressions protocolwith visual and audible prompts to stay clear of the patient. The“analyzing-stay clear” screen 1728 of FIG. 17c may be displayed atprompting step 1630 with the corresponding guidance to “stay clear ofthe patient” for further ECG analysis. Audible prompts are alsopreferably issued at prompting step 1630.

In a preferred embodiment, the AED is provided with the second ECGanalysis algorithm (PAS). At analyzing step 1628 and after “stay clear”prompts from step 1630 have issued, the second ECG analysis algorithmanalyzes the ECG to determine if the cardiac rhythm is shockable ornon-shockable. If PAS determines a “shock advised”, i.e. a shockablecardiac rhythm, then the method at charging/arming step 1634automatically begins charging and arming the shock delivery circuit forthe immediate delivery of electrotherapy. Exit step 1636 exits themethod after the AED is armed. Following exit step 1636, other methodsmay proceed such as looping back to analyzing step 1608, arming foradditional shocks, entering different protocols, or the like.

If PAS determines a “no-shock advised” at analyzing step 1628, 1632, theAED conveys the result and corresponding guidance to the user atprompting step 1638. Preferably, audible and visual instructions areprovided to resume CPR. ECG analysis also resumes at analyzing step 1608using the first ECG analysis algorithm.

An alternative embodiment for the right branch of method 1600 is tocontinue the use of the first ECG analysis algorithm after the “stayclear” prompts at prompting step 1630. The increased sensitivity of thefirst algorithm during quiet periods may allow detection of a shockablerhythm after the CPR noise signal component is eliminated. Analyzingstep 1628 thus may be used with the first ECG analysis algorithm insteadof the second ECG algorithm. Subsequent steps 1632, 1634, 1636, 1638 maybe similar to those previously described under this embodiment.

An AED with the elements as previously described may adopt the abovemethod having a truncation button. Accordingly, the AED necessarilyincludes a controller 30 which is operable to set the operating state ofthe defibrillator responsive to both of a sensed actuation of the inputtruncation button 854 and the underlying analyzed ECG signal.

The AED response to a sensed press of the Analyze option button may alsovary somewhat depending on the configuration of the device. For example,the Table 1 chart illustrates the functionality of the button duringvarious types of configurations and underlying ECG states:

TABLE 1 AED Patient ECG Press analyze button function configurationstate (contextual label and function) CPR first shockable Label: ChargeFn: charge for shock. CPR first Non-shockable Label: Analyze Fn: conductPAS analysis Analysis through shockable Button not available or PASanalysis CPR (continuous) Analysis through Non-shockable Label: AnalyzeFn: conduct PAS CPR analysis Scheduled shockable Label: Charge Fn:charge for shock. (uninterruptible CPR) Scheduled Non-shockable Label:Analyze Fn: conduct PAS (uninterruptible analysis CPR) Off Non-shockableAnalyze button as exists under PAS. Off shockable Analyze button asexists under PAS.

Modifications to the device, method, and displays as described above areencompassed within the scope of the invention. For example, variousconfigurations of the user interface displays and aural indicators whichfulfill the objectives of the described invention fall within the scopeof the claims.

1. An automated external defibrillator (AED) for use duringcardiopulmonary resuscitation (CPR) comprising: an input of an ECGsignal; a user interface having at least one of an aural instructionoutput and a visual display; an ECG analyzer in communication with theinput and operable to determine a shockable cardiac rhythm in thepresence of CPR-related signal noise artifact from the input; a memoryfor storing instructions related to a CPR rescue protocol that includesa period for providing CPR compressions; and a processor incommunication with the ECG analyzer and the user interface, theprocessor operable to issue instructions via the user interfaceresponsive to the determined shockable cardiac rhythm, wherein the ECGanalyzer is operable to determine the shockable cardiac rhythm in thepresence of CPR-related signal noise artifact from the input with asensitivity of greater than about 70% and a specificity of greater thanabout 95%, wherein the input comprises a stream of digitized ECG signaldata, and further wherein the ECG analyzer segments the ECG signal datacorresponding to a predetermined time segment, wherein the ECG analyzerfurther comprises a set of fixed-frequency band pass filters whichoperate to filter the CPR-related signal noise artifact from the ECGsignal data, wherein the ECG analyzer further comprises an algorithmwhich determines the shockable cardiac rhythm from both a measure of afiltered ECG signal data centered on one frequency at about 25 Hz and ofa second filtered ECG signal data centered on a second frequency ofabout 35 Hz, and wherein the ECG analyzer further determines that thecardiac rhythm is shockable if both the filtered ECG signal data and thesecond filtered ECG signal data are below respective predeterminedthresholds.
 2. The AED of claim 1, wherein the processor is furtheroperable to issue instructions to interrupt the CPR rescue protocolperiod if the ECG analyzer determines the shockable cardiac rhythm. 3.The AED of claim 2 wherein the user interface comprises one of a beeper,a flashing light, a speaker operable to issue aural prompts, and adisplay operable to graphically display visual prompts.
 4. The AED ofclaim 3, wherein the aural prompts further comprise instructions todiscontinue CPR, to deliver a defibrillating shock, and to resume CPR.5.-8. (canceled)
 9. The AED of claim 1, wherein the predeterminedthresholds comprise threshold numbers of data points within thepredetermined time segment.
 10. The AED of claim 1, further comprising:a high voltage charging circuit in controllable communication with theprocessor; a high voltage energy storage source electrically connectedto the high voltage charging circuit; and a shock delivery circuitconnected to the storage source, the delivery circuit operable todeliver a therapeutic shock via an output of the AED, wherein theprocessor controls the charging circuit to fully charge the storagesource in response to the determined shockable cardiac rhythm before theprocessor issues the instructions.
 11. The AED of claim 10, wherein theprocessor is further operable to arm the shock delivery circuit todeliver a therapeutic shock via the output simultaneously with theissuing of the instructions.
 12. The AED of claim 10, wherein theprocessor is further operable to arm the shock delivery circuit todeliver a therapeutic shock via the output and issue the instructionsonly after a predetermined period of CPR compressions.
 13. The AED ofclaim 10, wherein the user interface has both of the aural instructionoutput and the visual display, and further wherein the processorcontrols the user interface visual display to indicate the determinedshockable cardiac rhythm before the processor issues the instructions atthe aural instruction output.
 14. A method for controlling anelectrotherapy output from a defibrillator during the application ofCPR, comprising the steps of: receiving an ECG signal data stream fromtwo or more external electrodes in electrical contact with a patient,the ECG signal data comprising a cardiac signal characterized bycorruption from a CPR compressions noise artifact; filtering the streamof ECG signal data through a set of frequency band pass filters disposedto separate the cardiac signal from the CPR compressions noise signal;obtaining a stream of signal data corresponding to a predetermined timesegment; analyzing the separated cardiac signal to determine whether ashockable cardiac rhythm exists with a sensitivity of greater than about70% and a specificity of greater than about 95%; deciding that a shockis to be delivered by an electrotherapy delivery circuit based on theanalyzing step; arming an electrotherapy delivery circuit responsive tothe deciding step; and automatically issuing a user prompt to stop CPRand to deliver the electrotherapy at the completion of the arming step.15. The method of claim 1, wherein the analyzing step has a sensitivitygreater than about 95% and a specificity greater than about 98%.